Throws and throw

[Confused]

difference between throws ,throw and throwable

[Chetan Raju]

difference between throws ,throw and throwable

A method THROWS exception(s)
You throw an exception explicitly using THROW
Throwable is a super class of all exceptions / errors

[Confused]

thanks chetan.
but tell me one thing,
suppose i have a method called calculation() and that method is in a
try/ catch block and if any error occurs within that method then catch will show me the error like ArithmethicException ...something like that
and it is an example of throw ... which is happening implicitly ...
am I right ?

and when I want any of my method will throw me a particuler exception that time I can invoke a method like this

double calculation throws ArithmethicException()
{
}
am I right ...

[David Nemeskey]

Piyali:

Yes, basically:

public void main(String[] args) {
    try {
        calculate();
    } catch (ArithmeticException ae) {
        System.out.println("Exception in calculate: " + ae);
    } catch (Throwable t) {
        System.out.println("Throwable in calculate: " + t);
    }
}
 
double calculate throws ArithmeticException() {
    throw new ArithmeticException();
}

Of course, the code above is a bit silly; Throwables include Errors as well, not just Exceptions, so it may not be useful to catch them. Also, ArithmeticException is a runtime exception (descendant of RuntimeException), so it is not required to declare it in the method header. But doing so is a good idea, because the user of your API will get a better overview of what's happening.

[Confused]

Thanks David !
:-)

[Mattias Ahlin]

But normally you don't declare your RuntimeExceptions in the method header. Instead you declare them in the method's javadoc. See java.util.Vector for instance:

    /**
     * Returns the element at the specified position in this Vector.
     *
     * @param index index of element to return.
     * @return object at the specified index
     * @exception ArrayIndexOutOfBoundsException index is out of range (index
     *   < 0 || index >= size()).
     * @since 1.2
     */
    public synchronized Object get(int index) {
if (index >= elementCount)
    throw new ArrayIndexOutOfBoundsException(index);
 
return elementData[index];
    }

Otherwise your API will be polluted with RuntimeExceptions that the clients of the API normally shouldn't be catching anyway.
[ November 28, 2006: Message edited by: Mattias Ahlin ]